Construction And Application Of Molecularly Imprinted Electrochemical Sensor For Azo Colorants

Amaranth,Allura Red,New Coccine are the synthetic Azo colourants in the red food coloring.They are much popular in the food industry,due to their unique features including low cost,long-lasting color,good stability,and excellent solubility.However,excessive intake of them may cause adverse health effects,such as abnormal behavior in children,dizziness,anxiety,allergy,and even cancer.At present,though there have been many reports on the detection methods of this kind of food coloring,these methods are complicated,time-consuming and costly.Moreover,actual samples with complex substrates are treated by a tedious pretreatment,and these methods could be seriously interferred by interferers.Therefore,in this project,the molecular imprinting technology and electrochemical sensing technology were combined to fabricate a highly selective and sensitive molecular imprinted electrochemical sensor for red food coloring based on the nanomaterials or nanocomposites.The experimental mechanism,experimental conditions and application were studied in detail.The main contents and results are as follows:（1）The fabrication and application of amaranth molecular imprinting sensorA highly selective,stable,and robust electrochemical sensor was fabricated by electrodepositing a molecularly imprinted polypyrrole film in the presence of amaranth on the MWCNT surface.Then the template of amaranth was successfully eluted by applying potentiostatic scanning at negative potential in blank PBS,which is much faster and more eco-friendly in comparison with conventional methods.The molecularly imprinted polymers（MIPs）based electrochemical sensor was systematically investigated by scanning electron microscopy（SEM）,atomic force microscope（AFM）,X-ray diffraction（XRD）,cyclic voltammetry（CV）,and electrochemical impedance spectroscopy（EIS）.The resultant MIPs/MWCNTs modified glass carbon electrode（MIPs/MWCNTs/GCE）shows satisfactory electroactive surface area and charge transferred resistant.Together with specific recognition capacity toward amaranth,the electrochemical response signals were amplified remarkably at the MIPs/MWCNTs/GCE.Under the optimal conditions,the proposed MIPs/MWCNTs/GCE exhibits extraordinary analytical performance for amaranth determination,with two wide detection ranges(0.007μmol·L^-1 to 1.0μmol·L^-1,and 0.40μmol·L^-1 to 17μmol·L^-1).The detection limit（LOD）would be calculated as 0.4 nmol·L^-1.Moreover,the polypyrrole MIP films have high binding affinity and specific recognition towards amaranth molecules,enabling robust detection of amaranth in a complicated matrix with excellent selectivity,reproducibility,and stability.The proposed sensor achieves ultra-sensitive detection of amaranth in various fruit drinks with the acceptable recovery（95.0～97.7%）.（2）The fabrication and application of allura red molecular imprinting sensorThe prepared FeMoO₄ nanorods,which were synthesized by hydrothermal method,were composited with MWCNTs as composite.Then the composit were modified to the surface of glassy carbon electrode（GCE）.The allura red molecular imprinted polymer films were directlypolymerizedonFeMoO₄-MWCNTs/GCEby electropolymerization using allura red as templates and pyrrole as functional monomers.After the template molecules were removed,the allura red molecularly imprinted electrochemical sensor（MIPs/FeMoO₄-MWCNTs/GCE）with high sensitivity and good selectivity was obtained.The modified materials and the morphology of the imprinted polymerization were characterized by SEM and XRD.The preperation process of molecularly imprinted polymer electrochemical sensor was systematically studied by cyclic voltammetry.The detection conditions were investigated by the second derivative linear sweep voltammetry（SDLSV）.Under the optimal detection conditions,the sensor had a good linear response to allura red in the concentration range of 0.01～1μmol·L^-1 with the LOD of 6 nmol·L^-1.The method was applied to the high sensitivity determination of allura red in various fruit drink samples,and a relatively satisfactory recovery rate（96.4～101.0%）was obtained.This method has a potential application prospect in food detection.（3）The fabrication and application of New Coccine molecular imprinting sensorIn this study,nano-size Ce₂Mo₃O₁₃ was prepared by hydrothermal method,and was composited with MWCNTs as sensitization materials to modify the electrode surface.Using new coccine as template molecules and pyrrole as electropolymeric monomers,a highly selective and sensitive new coccine molecular imprinted electrochemical sensor(MIPs/Ce₂Mo₃O₁₃-MWCNTs/GCE)was fabricated by electropolymeric method.SEM and XRD were applied to analyzed the modified materials and characterize the morphology of the MIPs.Moreover,the fabrication process and detection conditions of the molecularly imprinted polymer electrochemical sensor were explored.Under the optimized detection conditions,the linear range of the sensor was 0.01～1μmol·L^-1 with the LOD of 7 nmol·L^-1.Inadditionally,the imprinting sensor had good selectivity,reproducibility and stability.The imprinted sensor was applied to the determination of new coccine in fruit drink samples with satisfying recoveries（97.0～100.7%,RSD<5%）.This strategy provided a highly selective and stable method for the high sensitivity determination of new coccine,and has a broad application prospect in the determination of other azo colourants.